In recent years, a standardization project “3GPP: 3rd Generation Partnership Project” has been discussing a standard regulation of a third generation (3G) mobile communication system. One of topics which has been discussed is a control signal transmission method of an upstream link (link in a direction from a terminal station to a base station).
For example, Non-Patent Document 1 proposes a method of encoding both ACK/NACK signals transmitted from multiple terminal stations and CQI (Channel Quality Indicator) signals at the upstream link with regard to each of the terminal stations. ACK/NACK signals are response signals of 1 bit for confirmation of transmission, ACK signal has a bit “1” used when responding positively, and NACK signal is a bit “0” used when responding negatively. CQI signal is a signal of 5 bits that reports a receiving level.
In a technique of Non-Patent Document 1, ACK/NACK signals and CQI signals are encoded by using “CAZAC (Constant Amplitude Zero Auto Correlation)” code. In this conventional technique, the phase shift amount of CAZAC code used for encoding is varied with regard to each of the terminals. It should be noted that the CAZAC code is a code that has constant amplitude and no autocorrelation.
However, the above-described conventional technique assigns CAZAC code of the different phase shift amount to each of the terminals, but has a problem in which a number of the terminal stations to which the code can be assigned is small.    [Non-Patent Document 1] 3GPP, R1-062742, NTT DoCoMo et al., “CDM-based Multiplexing Method of Multiple ACK/NACK and CQI for E-UTRA Uplink”, Oct. 9-13, 2006